The liquid level gauge according to the invention aims to achieve, with a simpler construction, smaller size and lower cost, the control of level changes of the liquid in a liquefied gas tank. Heretofore, this control has been difficult, particularly in case of relatively small tanks or bottles, as the existing devices, even if comprising magnetic elements, are very clumsy due to the use of rotating drive members, rocker arms with floats and pivoted counterweights for the drive rod or the like. Also, a system is known wherein the movement of a float is transmitted from the inside to the outside by means of two magnetic pastille-shaped elements disposed at a pre-established inclination, one inside and the other outside; however, this system entails a complicated and expensive construction. Therefore, this problem has not yet been solved in a simple, dependable and economic manner, i.e. with a device adapted for industrial mass-production and extensive marketing together with the valves used in this field, said valves constituting, after suitable modifications, the supporting member for said device. The level gauge according to the invention solves this problem satisfactorily in that it comprises a float having a rocker arm with no counterweight and a control cam with a single pivot, and the magnetic actuation of the external dial-and-hand indicator is effected by a single internal cylindrical magnetic element (made from a bar) actuating, rather than a second magnetic element, a small-sized cross-shaped member mounted on the freely rotatable spindle of the indicating hand and having a needle-shaped ferrous member (preferably made of steel), so as to ensure, despite of the single construction thereof, a reliable operation even for many years.